The present invention relates to power amplifiers which are used in digital wireless telephone applications. Specifically, a power amplifier which has improved reflective power handling capabilities is disclosed.
Portable telephone wireless communication systems employ a battery powered low power radio frequency transmitter circuit coupled to a portable antenna. The usual arrangement includes a telescopic vertical antenna which is fixed to the portable telephone. A problem experienced by the wireless portable telephone is that significant levels of reflected power are experienced due to antenna orientation, and the environment in which the portable telephone is used. The high levels of temporary VSWR seen by the power amplifiers can, besides reducing the effective radiated power, damage the transistors in the final power amplification stages, and, additionally reduce the linearity of the output amplifier. If the reflected power has a constant phase amplitude, due to an unchanging antenna orientation and environment, a matched network could be provided to reduce the reflected power and VSWR. However, the phase and amplitude of the reflected power are constantly changing with the antenna orientation and environment. Accordingly, any attempt to try and match the output amplifier impedance to the antenna impedance must be done dynamically to compensate for the changes in reflected power amplitude and phase.
The present invention has been provided to avoid the consequences of reflected power which continuously changes phase and amplitude.